DTH-hammer drilling device and overburden drilling method

ABSTRACT

The invention relates to a DTH-hammer drilling device, comprising a down-the-hole- (DTH-) hammer ( 6 ) with a percussion drill bit ( 9 ), a drill pipe ( 2 ) with a waste conduit for the cuttings and at least one supply conduit for the flushing medium and a flushing medium supply device, wherein a seal ( 18 ) for sealing the borehole against the borehole opening is provided in a fixed distance from the drilling head ( 6 ), or wherein a casing tube ( 12 ) is connected to the drill bit ( 9 ). The invention further relates to an overburden drilling method, comprising rotating a drill bit ( 9 ), supplying an energy transfer medium through a drill pipe ( 2 ) to the rotating drill bit ( 9 ) for transmitting a percussive action thereonto, dragging a casing tube ( 12 ) along with the drill bit ( 9 ) and flushing away cuttings through the drill pipe ( 2 ).

The present invention relates to a drilling device, in particular by use of a down-the-hole hammer, and a drilling method in particular for overburden drilling.

Drilling devices denoted “down-the-hole hammer” have a rotating percussion drilling head which is lowered into the borehole.

Other terms used therefor are “Inhole-hammer” and “DTH-hammer”, which term will be used in the following.

In the context of this application, overburden drilling is intended to denote a drilling method wherein a tube providing a casing for the borehole is dragged along at least in the region of the bottom of the borehole.

In the published German patent application DE 43 10 726 A1 a drill rig with a DTH-hammer is described wherein compressed air is supplied as a flushing medium from a peripheral conduit of the drill rig to a centre of the drill bit using a distributor, and the cuttings are lifted through a conduit arranged centrally in the drill rig.

The known device further has a skirt open at its lower end in the area of the hammer, through which the compressed air enriched with the cuttings is fed to the distributor.

In US patent application US 2005/0103527 A1 a dual wall drill pipe is described, the inner part of which is formed as a hose through which the cuttings are transported upwardly, while drilling mud is urged downwardly through the space between inner and outer hoses.

In the International application WO 02/081856 A1 a drilling head is described, in which the flushing medium is supplied outwardly to a rim of the drill bit, and the cuttings are transported from a central part of the drill bit to a periphery of the drilling head.

It has been found that the known drilling devices on the one hand have a need for high flushing medium flow rates, and that on the other hand, in some applications the drill depth is insufficient, the drill speed is partly not satisfactory, or the provided borehole diameter is small.

It is therefore an object of the present invention to provide a drilling device and method overcoming the drawbacks of the prior art; e.g., by having an increased efficacy, i.e. provide a greater drill depth or a larger borehole diameter faster or with lesser flushing medium flow rates.

According to a first aspect, the drilling device according to the invention has a DTH-hammer with a percussion drill bit, a drilling tube with a waste conduit for the cuttings and at least one supply conduit for the flushing medium, and an overburden tube connected to the drill bit.

According to an embodiment of the invention, above a distributor, a ring is mounted preferably rotatably around the drill pipe, on which ring at least one, preferably two to five disks are arranged as a seal. In particular, rubber disks separated by smaller diameter plastic disks are used, where an outer diameter of the rubber disks corresponds to, i.e. is about equal to or slightly larger than, an inner diameter of the overburden tube. The tile of rubber and plastic disks is preferably held together by two steel disks of a lesser diameter, which are screwed together. In an axial direction, the seal assembly of the disks and a ring supporting same is preferably secured by a flange or the like.

By this measure, it is achieved that flushing medium pressure losses through gaps in the rock are reduced. An additional pressure loss due to the borehole volume's increase during drilling is avoided. As a result, the energy transfer medium throughput necessary to drive the hammer is sufficient to serve as a flushing medium after leaving the hammer, largely independently from the nature of the surrounding rock (gaps, water).

Furthermore, the invention provides a method of overburden drilling using air lifting. According to this aspect, the method according to the invention comprises supplying the flushing medium, in particular peripherally to the carrying away of the cuttings, at least over a predominant part of the drilling depth, and dragging along an overburden tube adjacent the surrounding rock. Herein, it is preferred that the overburden tube does not rotate, or rotates more slowly relative to the surrounding rock than a centrally arranged drill pipe for the supply and carrying away of the flushing medium.

In a preferred embodiment, the method according to the invention further comprises the sealing of the borehole bottom against the borehole opening, and in particular the dragging along of the sealing packing. The packing rotates relatively to the surrounding rock at most with the speed of the drill pipe, and at least with the speed of the overburden tube.

According to another aspect, a rotative-percussive drilling method is provided, which comprises the supplying of energy by means of an energy transfer medium to a hammer arranged in the borehole concurrently with rotating the hammer.

According to a still further aspect, a drilling device according to the invention has a reduced free cross-section around the hammer at most ten times as large as the free cross-sectional area within the waste conduit.

Further advantageous embodiments and details are disclosed in the dependent claims, the subsequent description and the enclosed drawings. The claims are intended to be a non-limiting approach to defining the invention in general terms.

The drawings show:

FIG. 1 a drilling device according to the invention in a lengthwise sectional view;

FIG. 2 a drilling device according to the invention in cross-sectional view;

FIG. 3 a plug as used with the invention in cross-sectional view;

FIG. 4 a sketch overview of a drilling device according to the invention;

FIG. 5 another drilling device according to the invention in a partial lengthwise sectional view.

In the embodiment according to FIGS. 1 and 2, the drill rig 1 comprises a drill pipe 2 with a central waste conduit 3 and a peripherally arranged air supply conduit 4. To the lower end of the drill pipe 2, a connecting piece 5 is welded, in which a DTH-drill head 6 is screwed with its central connector 7, which comprises a compressed air supply opening 8 through which the DTH-drill head 6 is supplied with compressed air for driving its percussion drill bit 9. The diameter of the drill bit 9 is larger than the diameter of the drill pipe 2 and is larger than the diameter of the drive part of the DTH-drill head 6. In the connecting piece 5, a supply conduit section 10 leads from the centrally arranged waste conduit 3 of the drill pipe 2 obliquely downwards to a laterally arranged inlet opening 11. An air duct section 13 leads from the peripheral air conduit 4 of the drill pipe 2 via a connection annulus 111 to a central area of the connector 7 of the drill head.

The percussion drill bit 9 is driven with compressed air, which in the example is provided by a compressor station 60 located adjacent the borehole opening, to perform a hammering action while being rotated by the drill rig 1. The drill bit 9 includes a central pilot bit 9 a and a surrounding reaming bit 9 b. The pilot bit 9 a and the reaming bit 9 b are connected to one another by a releasable bayonet coupling. The reaming bit 9 b is rotatably, and preferably coaxially, connected to an overburden tube 12 via a casing shoe 15, thereby dragging along the overburden tube 12 during drilling. The air flowing from the borehole bottom back to the borehole opening, aided by water already present in the borehole or additionally supplied, serves as a flushing medium and maintains a flow velocity in the central waste conduit 3 sufficient to carry away the cuttings. The flow velocity exceeds 30 m/s, and is preferably 70-80 m/s, in particular about 75 m/s.

In the embodiment according to FIG. 1, the drill bit 9 further comprises a supply duct section 41 for compressed air 42 flowing from the hammer 6 into the drill bit 9, a supply duct 43, a waste duct 44, a bypass (choke shunt) 45 and a waste discharge duct 46 for compressed air 47 flowing back towards the surface. At the face of the drill bit 9, drill elements 50 a and 50 b of the pilot and reaming bit, respectively, are arranged. The reaming bit 9 b is, on the one hand, releasably reconnected to the pilot bit 9 a via the securing elements 51, 52, 53, and on the other hand is rotatably connected to the casing shoe 15, so that the reaming bit 9 b is able to drag along the casing shoe 15 as well as the overburden tube 12 welded thereto. Thereby, the overburden tube 12 does not rotate, or rotates much more slowly relative to the surrounding rock than the drill bit 9, depending on the friction provided by the borehole wall and the torque applied through the drill bit 9.

Compressors 60 having a combined throughput capacity of 30 to 80 m³/min, preferably 50 to 70 m³/min, serve as the compressed air supply for an 18″-DTH-hammer and a drill pipe having 200 mm outer tube diameter and 125 mm inner tube diameter. With increasing drilling depth and grain size of the cuttings, accordingly larger air supply rates are used. Also, the supply rates scale with hole diameter.

The borehole is clad with the overburden tube 12 at least in the area of the hole bottom and beyond the hammer 6. Above the connector 5, a plug 18 (FIG. 3) is set as a sealing packing which tightly fits between the overburden tube 12 and the drill pipe 2 and is carried downwards during drilling along with the drill pipe 2. The plug 18 in the embodiment shown comprises three resilient disks 20 supported in a spaced apart manner by two rigid disks 22 of a lesser diameter. Two to four or five rubber disks are preferred, spaced apart by a number of plastic disks one less. The pile of rubber disks and plastic disks is held on both sides by steel disks 24 of the same diameter as the plastic disks 22, and six threaded bolts 28 passing through bores 26 in the disks, and nuts. The stack of disks is arranged on a mounting ring 30 and fastened with bolts 32 accessible through a flange hole 31, whereby the mounting ring 30 is rotatably mounted on the drill pipe 2 and is fixed in axial direction by a fixing ring 34 welded to the drill pipe 2. By this arrangement, the mounting ring 30 does not rotate with the drill pipe 2, or possibly rotates slowly, while the rubber disks 20 contact the inner wall of the overburden tube 12. Relative to the surrounding rock, the sealing disks of the plug 18 rotate with a speed of at least that of the overburden tube and less than that of the drill pipe 2. In an alternative embodiment (not shown), instead of the disk pile, an inflatable tube ring (“packer”) is arranged on the mounting ring 30. In another not-shown variant, no overburden tube is present, and the rubber disks accordingly seal against the borehole wall.

As the overburden tube 18, for example a pipe of dimensions 711 (28″)×8 mm is used, into the inner diameter of which of 695 mm, the rubber disks 20 of the plug are fit. The rubber, steel and plastic disks of the plug 18 each have a thickness of 15 mm. These disks are mounted on a bronze ring 30 as shown in FIG. 3, the bronze ring 30 in turn being rotatably sled onto the drill pipe 2 of outer diameter 200 mm, and secured in axial direction by a fixing ring 34.

Above the connector 5, a drill collar 36 (see FIG. 4) is arranged for damping the upward hammer action and for thereby directing hammer action downwardly. The drill collar 36 is, for example, formed as a part of the drill pipe 2 with an outer sleeve filled with lead. The plug 18 is arranged above or preferably, below the drill collar 36.

In the above described example, the overburden tube is a contiguous pipe string, which is continuously appended during drilling and may be left in the borehole after drilling. In an alternative drilling device, the overburden tube is not appended beyond the plug, but is closed at its upper end by a e.g. frustoconical lid piece. In this case, alternatively the lid piece is formed as a sealing packing, so that the plug is dispensible. Herein, the lid piece rotatably seals against the drill pipe.

In another embodiment (see FIG. 5), a sleeve tube 14 surrounding the hammer 6 is arranged below the lateral inlet opening 41, wherein the sleeve tube is closed below the inlet opening 41, preferably at its lower end, and preferably is double-walled. In this example, the sleeve tube 14 extends upwardly somewhat beyond the inlet opening 41, namely up to the upper rim of the connector 5, wherein a duct 115 is formed in the sleeve tube 14 for the lateral inlet opening 11. Thereby, the flushing medium is forced to flow through the constricted annular space (outer shaded area in FIG. 2) between the sleeve tube 14 and the overburden tube 12. Due to the constricted free cross section, the flow speed at the height of the hammer 6 is increased so as to secure the blowing out of the cuttings.

In the method according to the invention, the drill bit 9 is rotated, while an energy transfer medium, e.g. a portion of the flushing medium, is supplied through the drill pipe 2 to the hammer 6 for transmitting a percussive action onto the rotating drill bit 9. Along with the drill bit 9, an overburden tube 12 and a sealing packing 18 between the overburden tube 12 and the drill pipe 2 is dragged, and the cuttings are flushed away through the drill pipe 2. The overburden tube may be continuously supplemented at its upper end at the borehole opening, or may the closed at its top after mounting the seal. In the former case, the overburden tube may be left in the borehole after conclusion of the drilling, or may be taken out of the hole. In the latter case, there is the advantage that the frictional resistance provided by the dragged-along overburden tube remains independent of the drill depth, and therefore does not set a substantial limit thereto.

The drilling methods of the invention have the advantage that by carrying along the plug 18 above the air distributing connector 5 for redirecting the flushing medium, and by dragging along an overburden tube 12, a sufficient pressure gradient between the borehole bottom and the borehole opening for blowing out the cuttings, is maintained: On the one hand, the flushing medium cannot escape into gaps in the surrounding rock, and on the other hand, the volume to which the pressure is applied remains constant during drilling, and is relatively small.

In another preferred embodiment, the flow-through cross-section for the cuttings is constricted in the area of the hammer, if necessary by means of a sleeve tube surrounding the hammer, in such a manner that the cross-section is at most 10 times as large as the inner cross-section of the waste conduit of the drill pipe (inner shaded area in FIG. 2), on the other hand preferably not less than same, in particular is at least four times as large, and particularly preferably is six to eight times as large, such that even coarse cuttings can pass through. The necessary constriction may also be achieved by using an oversized hammer, which is preferably choked below its nominal operation pressure (e.g. <6.9 bar) so as not to damage the drill bit due to its nominally excessive energy output. Also, the cross-sectional shape of the constricting device may be other than cylindrical, e.g. may have an undulating circumference providing a number of alternating more and less constricted portions, respectively.

It is preferred to form the overburden tube, the waste conduit of the drill pipe and the optional sleeve tube circular-cylindrically, in particular concentrically. In this case, the three lengths (see FIG. 2):

-   -   A=outer diameter of the hammer, or of the sleeve tube arranged         around the hammer if present;     -   n·B=1.5 to 4 times, preferably 2.5 to 3 times the inner diameter         B of the waste conduit for the flushing medium above the         distributor; and     -   C=inner diameter of the overburden tube, or of the bore hole if         no overburden tube is present in the bottom hole section,         when arranged to a geometrical shape, form an acute-angled         triangle or, preferably, a right-angled triangle with sides A,         n·B und C. Also, e.g. C>5.5 B, preferably C>n·B.

By these measures it is ensured that the cuttings are blown peripherally past the hammer into the drill pipe, and do not accumulate in the borehole.

The optional sleeve tube is preferably single or dual walled and may comprise a duct or a cut-out connecting the inlet opening of the distributor with the annular space surrounding the sleeve tube. Further, the sleeve tube may extend at its upper end up to the drill pipe or the distributor, and at its lower end down to the lower end of the hammer. Preferably, the lower end of the device or tube is closed, but it suffices if the closure is located below the distributor inlet.

Thereby, it is achieved that the cuttings entrained in the flushing medium flow around the sleeve tube to the inlet opening of the distributor with a velocity sufficiently high so as to accelerate the cuttings to its lifting speed.

In a preferred embodiment, the drilling method is carried out in a first section, at a relatively larger hole diameter, using such a sleeve tube; and after reaching a certain depth of the borehole, a second section is drilled with a smaller hole diameter without the sleeve tube, or with a smaller diameter sleeve tube. Into the upper, wider hole section, there can e.g. be installed a detention casing. In this manner, the entire drilling operation can be accomplished with largely the same components and with accordingly reduced requirements in terms of space, time and cost. 

1. A DTH-hammer drilling device, comprising: a down-the-hole- (DTH-) drilling head with a percussion drill bit; and a drill pipe with a waste conduit for cuttings and at least one supply conduit for a flushing medium, wherein a seal is provided at a fixed distance from the drilling head for sealing the DTH-hammer drilling device against the borehole opening.
 2. The DTH-hammer drilling device according to claim 1, further comprising a casing tube rotatably connected to the percussion drill bit.
 3. A DTH-hammer drilling device, comprising: a down-the-hole- (DTH-) drilling head with a percussion drill bit; and a drill pipe with a waste conduit for the cuttings and at least one supply conduit for flushing medium, further comprising a casing tube connected to the percussion drill bit.
 4. The DTH-hammer drilling device according to claim 3, further comprising a seal for sealing the DTH-hammer drilling device against the borehole opening.
 5. The DTH-hammer drilling device according to claim 2, further comprising a hammer, a casing tube and a sleeve tube arranged between the hammer and the casing tube.
 6. The DTH-hammer drilling device according to claim 5, wherein the sleeve tube is closed below an entrance of the waste conduit.
 7. A DTH-hammer drilling device, comprising; a down-the-hole- (DTH-) drilling head with a percussion drill bit; a drill pipe with a waste conduit for the cuttings and at least one supply conduit for a flushing medium; a hammer and a sleeve tube arranged around the hammer and closed below an entrance of the waste conduit.
 8. The DTH-hammer drilling device according to claim 7, further comprising a casing tube connected to the drill bit.
 9. The DTH-hammer drilling device according to claim 8, wherein the casing tube and the sleeve tube have circular-cylindrical shape.
 10. The DTH-hammer drilling device according to claim 9, wherein the casing tube and the sleeve tube are concentrically arranged.
 11. The DTH-hammer drilling device according to claim 10, wherein an outer diameter A of the sleeve tube, an n-fold inner diameter n·B of a circular-cylindrical waste conduit, and an inner diameter of the casing tube fulfill the condition that a triangle with sides A, n·B and C is right-angled or acute-angled, wherein 1.5<n<4.
 12. The DTH-hammer drilling device according to claim 1, further comprising a flushing medium supply device.
 13. The DTH-hammer drilling device according to claim 1, wherein, in a region of the hammer, a free sectional area around the hammer is at most ten times as large, and at least as large as a free cross sectional area of the waste conduit.
 14. The DTH-hammer drilling device according to claim 13, wherein the free cross sectional area around the hammer is at least four tines as large as the free cross sectional area of the waste conduit.
 15. The DTH-hammer drilling device according to claim 1, wherein the waste conduit is surrounded by the at least one supply conduit.
 16. The DTH-hammer drilling device according to claim 1, wherein the seal comprises two to five spaced apart resilient disks.
 17. The DTH-hammer drilling device according to claim 16, wherein said rubber disks are separated by at least one of less-resilient and plastic disks.
 18. The DTH-hammer drilling device according to claim 17, wherein a diameter of the plastic disks is less than a diameter of the rubber disks.
 19. The DTH-hammer drilling device according to claim 16, wherein the disks are arranged on a mounting ring rotatably arranged around the drill pipe.
 20. An overburden drilling method, comprising; rotating a drill bit; supplying an energy transfer medium through a drill pipe to the rotating drill bit for transmitting a percussive action thereonto; dragging a casing tube along with the drill bit; and flushing away cuttings through a waste conduit of the drill pipe
 21. The drilling method according to claim 20, further comprising compressing air for providing the energy transfer medium.
 22. The drilling method according to claim 20, wherein the flushing away of the cuttings is effected at least partly by the energy transfer medium after its acting on the drill bit.
 23. The drilling method according to claim 20, wherein the cuttings are lifted through the drill pipe with a speed of at least 50 m/s.
 24. The drilling method according to claim 20, further comprising arranging a sleeve tube around a hammer, an flushing away the cuttings around the sleeve tube and then into the waste conduit.
 25. The drilling method according to claim 24, wherein a first drilling section is carried out with the sleeve tube arranged between the hammer and an easing tube for drilling a larger diameter first borehole section, and a second drilling section is carried out without the sleeve tube for drilling a smaller diameter second borehole section.
 26. A drilling method, comprising: rotating a drill bit; supplying an energy transfer medium through a drill pipe to the rotating drill bit for transmitting a percussive action thereonto; and flushing away cuttings through a waste conduit of the drill pipe, wherein a first drilling section is carried out with a sleeve tube arranged around a hammer for drilling a larger diameter first borehole section, and a second drilling section is carried out without the sleeve tube for drilling a smaller diameter second borehole section, wherein in the first borehole section, cuttings are flushed away around the sleeve tube.
 27. The drilling method according to claim 26, further comprising dragging along a casing tube along with the drill bit.
 28. The drilling method according to claim 20, further comprising dragging along a packing between the casing tube and the drill pipe, or between the borehole wall and the drill pipe. 